Habitat fragmentation and biological invasions are widely considered to be the most significant threats to global biodiversity, and synergistic interactions between these processes have the potential to cause even greater biodiversity loss than either acting alone. The objective of my
study was to investigate the effects of fragmentation on plant communities in native forest fragments, and to examine potential interactions between these effects and invasions by exotic
plants at multiple spatial scales. I examined edge, area and landscape effects on plant invasions using empirical data from fragmented landscapes on the West Coast of New Zealand. My research revealed significant interactions between the amount of native forest cover in the landscape and the strength of edge and area effects on plant communities in forest fragments. The dominance of
exotic plants in the community was highest at forest edges and decreased towards fragment interiors, however the interiors of very small fragments were relatively more invaded by exotic
plants than those in larger fragments, reflecting a significant interaction between edge and area effects. Similarly, exotic dominance increased in more heavily deforested landscapes, but this effect was only apparent in very small fragments (<2 ha). The combined effects of small fragment
size and low forest cover in the landscape appear to have promoted invasions of exotic plants in
very small remnants.
I explored the mechanisms underlying edge-mediated invasions in forest fragments and examined whether propagule availability and/or habitat suitability may be limiting invasions into fragments. Experimental addition of exotic plant propagules revealed that landscape forest cover interacted
with edge effects on germination, growth and flowering rates of two short-lived, herbaceous species, and this appeared to be driven by elevated light and soil phosphorus levels at edges in
heavily deforested landscapes.
I also examined the role of traits in influencing plant responses to forest fragmentation. Different traits were associated with exotic invasiveness in edge and interior habitats of forest fragments, indicating that the traits promoting invasiveness were context dependent. Traits also had a major
influence on responses of native plants to forest fragmentation, with generalist species appearing to benefit from fragmentation, as they can utilise both forest and open habitats, whereas native forest specialists have been negatively impacted by fragmentation.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/3218 |
| Date | January 2009 |
| Creators | Hutchison, Melissa Alice Sarah |
| Publisher | University of Canterbury. School of Biological Sciences |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Melissa Alice Sarah Hutchison, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
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